Spent hours trying to fix this on my own. 
 
Updated to new latest Melodyne and now my project which uses Melodyne has no audio output to the audio interface. 
 
I can see the meters within Sonar registering, including in the Master bus, and I receive no error warnings. 
The master bus still shows it is connected to the audio interface.
If I open same project in 'safe mode' and disable Melodyne as a plug-in, the sound comes through. 
If I open another project and add Melodyne to a track, sound is fine.
 
Please help me.  It is a massive project and I don't have the heart to start from scratch.

EDIT, nevermind . . . just noticed you are on X3, so my suggestion probably won't work.

Actually, sometimes it does work -- and sometimes not.  Very sporadic.  But thanks for the idea.  Still working on a true fix, but in case anybody is wondering, this is what was suggested:
 
"toggling the global FX button on the control bar on and off"

So here is what I am currently doing:
1. Start PC. 
2. Start Sonar.
3. Load big project.  Hit play.  See meters moving but no sound. Try turning off global FX -- no difference.  Reset audio engine and MIDI.  Still no sound.  
4. Open Quad Capture control panel.  Select 'Initialize...' under <device> menu.
5. Go back to Sonar.  Hit play.  Still no sound.  Turn off FX with global bypass.  *Now* there is sound.  Turn FX back on -- and sound still works.
6.  Work in project for awhile until I try to do something with audio (start recording a new track, move a recorded bit from one track to another, etc.) Sound from speakers stops.  Meters still move.
7.  Try global FX reset, bunch of other stuff -- usually makes no difference.  Return to step 1.  
 
What should take me fifteen minutes can take hours.  Given what I still plan to do with this piece, one week's work may take more than a month.  What kills me is I see the meters moving, so it is not dropouts or pops or anything.  I went with the Quad Capture because I figured it would be rock solid.
 
Suggestions?   

Which version of Melodyne did you recently upgrade to ? (Essential, Editor, Studio . . . version 4 ?)
I personally found it quite annoying that when I upgraded from Melodyne 3 to Melodyne 4 . . . version 3 got totally removed / deleted, and I recall it taking a while to get the new version working right, but once I did it now works flawlessly in all projects.
 
Is it possible to save the project out, without the Melodyne tracks, renaming it, then cut and paste the Melodyne tracks from the old project back into the new version of the project ? I've done this before to rescue old projects that have some unknown corruption, though I can't say I've specifically cut and pasted bad Melodyne tracks. Just a thought, since there don't seem to be any other forum ideas here so far. I've even had instances where a corrupted master bus from an older project caused troubles, which I could fix by just deleting the master bus, then inserting a new one.
 
Another thing I might suggest, is downloading / installing the Sonar Platinum demo (I have X2, X3 and Platinum running on the same system, and I don't think they interfere with each other) . . . then try the project out using Platinum version, see if the same troubles exist, this might better point you to if it's a Melodyne version , or Quad Capture issue ?
 
Just some ideas, hope some of it is helpful.